Hagel's confirmation to the Senate remains uncertain, particularly in light of his rocky performance at Thursday's hearing.

Pro-Israel groups and Republican defense hawks have leveled harsh criticism against Hagel in recent week. In addition to the "Israel lobby" comment, their grievances include Hagel's past opposition to multilateral sanctions on Iran and his support for open negotiations with Hamas.

While most Senate Democrats have indicated they will vote to confirm Hagel, despite these reservations, it is not clear if he will get enough Republican support to avoid a filibuster.